Six months after President Obama vowed to change his administration's approach to lethal drone missile strikes, the pace of aerial attacks has fallen sharply, thanks in part to stricter targeting criteria.

Obama also promised to make the drone campaign more transparent. But a blanket of secrecy thus far has remained firmly in place.

The Democrat-led Senate Intelligence Committee voted on Nov. 5 to require the administration to disclose how many civilians and militants were killed by drones each year. That tally has never been publicly available.

The panel also voted to impose additional intelligence demands before the White House could authorize a drone strike against a U.S. citizen or resident alien. Drones have killed five Americans since 2002, although only one, Al Qaeda operative Anwar Awlaki, was officially marked for death.

"The American people should be given basic facts about mistakes when they are made, and they should also be given the rules that the government must follow when targeting and killing an American involved in terrorist activities," Sen. Ron Wyden (D-Ore.), a committee member, said in a statement.

The proposed restrictions, however, part of a broader intelligence bill, may not survive. Republicans on the Senate panel voted for the bill, but most opposed the drone amendments. Key lawmakers in the GOP-controlled House also oppose the provisions.

The White House has yet to take a position. Caitlin Hayden, spokeswoman for the National Security Council, said the administration already was transparent concerning drones.

"The president has committed to undertaking these activities with the greatest possible transparency, and we will continue to share as much information as possible with the American people, the Congress and the international community," she said.

In a speech in May at National Defense University, Obama said he had signed a policy directive that set new standards before the White House would approve targeted killing by drones.

Obama said the CIA had to show that a proposed target posed a "continuing imminent threat" to Americans, rather than a "significant threat," the previous standard. In addition, no attack would be ordered without "near certainty" that civilians would not be harmed, the president said.

The number of strikes already had fallen before May, but the new rules served to cut the frequency further.

The Long War Journal, which tracks drone attacks through local news reports, has counted 22 strikes this year in Yemen, down from 42 last year. It has counted 25 attacks in Pakistan this year, down from 46 last year and a peak of 117 in 2010. A single strike has been reported in Somalia this year.

Administration officials have said drone strikes have killed relatively few civilians, but have refused to say how many. The Long War Journal says 11 civilians have been killed in Pakistan this year and two in Yemen; other estimates are higher.

In June, a drone-launched missile hit an SUV carrying an Al Qaeda commander in Yemen. CIA officers didn't realize that his younger brother also was in vehicle, according to U.S. officials who would not be named because the operation is classified. The CIA later put the victim's age at between 6 and 13.

The CIA has given a classified briefing to Congress on the death, but has refused to acknowledge it publicly. The NSA's Hayden declined to comment.

Sen. Dianne Feinstein (D-Calif.), chairwoman of the Senate Intelligence Committee, said the number of noncombatant deaths was "significantly lower" than critics claimed. She said she had urged the White House to disclose the data "so the American people know how careful these strikes have been."

In part, drone strikes have declined because there are fewer identified terrorist leaders to hit. In Pakistan, the core leadership of the Al Qaeda network founded by Osama bin Laden has been decimated, although remnants are still active.

Al Qaeda in the Arabian Peninsula, which is based in Yemen, has weakened but is still virulent. Nine U.S. drone strikes were launched against the group in August after authorities detected a plot against U.S. embassies. But the pace has dropped to about two a month since then.

Harold Koh, who served as State Department legal advisor in Obama's first term, said in an email that the new targeting standards had "disciplined" the drone program.

But Koh, now a professor at Yale Law School, said he saw "little or no movement" on making the program more transparent, a goal he believes is necessary to boost the program's legitimacy abroad.

In May, White House aides indicated that the Pentagon would take over at least some covert drone operations from the CIA. The military operates under different legal statutes than the CIA, and can provide more information to the public.

That plan has stalled, however, due to logistical, bureaucratic and legal concerns.

The CIA is resisting giving up its drones, especially in Pakistan, where the government almost certainly would oppose U.S. military operations. Some counter-terrorism officials also worry that the Pentagon won't be able to act as quickly as the CIA.

Leon E. Panetta, who served as CIA director from 2009 to 2011 and as secretary of Defense from 2011 to 2013, favors shifting more drone operations to the military.

"We made a great deal of progress at the CIA, and it was a very effective operation in terms of establishing targets and conducting very specific strikes at going after core Al Qaeda leadership," he said on CBS' "Face the Nation" on Nov. 10.

The Pentagon "is beginning to develop that kind of capability," he said.

"I think ultimately the more we can probably put into the military the better, because it's a much more open process."